1. Field of the Invention
The present invention relates to an optical head for recording information on an optical disk or reproducing information from the optical disk.
2. Description of the Prior Art
In recent years, with the spread of optical disk drives as an external storage for consumer equipment or computers, demand for a compact and flat optical disk drive had increased.
As a result of miniaturization and thinning, the optical disk drive has a large packaging density which gives rise to a problem of low efficiency of assembling and adjusting operation.
More specifically, an optical head is a central and main component of the optical disk drive and has a considerable effect on the miniaturization and thinning of the optical disk drive. It is, therefore, desirable that the optical head should be constructed compactly and less thick without lowering the efficiency of assembling operation.
Conventional optical heads, as shown in FIG. 5 of the accompanying drawings, include a semiconductor laser unit 1 having, as a single unit, a collimating lens, a semiconductor laser and a high-frequency superimposed circuit for exciting the semiconductor laser, and a detector 2 for detecting the reflected light from an optical disk and producing a servo signal and an information signal. The semiconductor laser unit 1 and the detector 2 are screwed to a side wall of a head box 3. The head box 3 has on its bottom surface a plurality of lands 4 through 8 to which optical components such as prisms and mirrors are bonded. The land 4 supports thereon a beam shaping prism 9. The land 5 supports thereon a composite beam splitter 10 comprised of a combination of a beam shaping prism and a deflection beam splitter. The land 6 supports thereon a mirror 13 for directing light from the semiconductor laser unit 1 to an objective lens 12 of an objective lens actuator 11. The lands 7 and 8 support respectively thereon an analyzer 14 and a split prism 15 for directing the reflected light from the optical disk to the detector 2. The head box 3 is closed by a cover 16 screwed to the head box 3. The objective lens actuator 11 is screwed to the cover 16 in such a condition that the center of the intensity distribution of light coming from the semiconductor laser unit 1 is located at the center of the objective lens 12.
A pickup lens 17 is secured to the bottom surface of the head box 3 along a slit 18 in the bottom surface by means of screws (not shown) extending from the underside of the head box 3.
The prisms and mirrors 9, 10, 13-15 are made of plastic or glass. The head box 3 is an aluminum die-cast, in general. In view of the materials used, an ultraviolet-curing adhesive is generally used for bonding the prisms and mirrors 9, 10, 13-15 and the head box 3.
With this construction, the conventional optical head encounters difficulties in assembly when the prisms and mirrors are bonded to the lands 4-8 of the head box 3.
The prisms and mirrors 9, 10, 13-15 must be bonded while keeping the positional relationship in a highly precise manner. To this end, a jig is placed on the top or the side of each optical component for positioning the same. However, since the lands to which the optical components are to be bonded are surrounded by a relatively high side wall of the head box 3, a smooth placement or setting of the jig is impossible. The high side wall of the head box 3 further limits the degree of freedom in designing each jig and hence the resultant jig is complex in construction and uneasy to handle.
Furthermore, when all positioning jigs are set, an open end of the head box 3 is substantially closed by the jigs. In this condition, the bonding surface is no longer irradiated with ultraviolet rays which is used for curing the adhesive. In view of this difficulty, bonding operation is performed repeatedly from one optical component to another. Accordingly, the assembling efficiency of the conventional optical head is considerably low. The foregoing problems become more significant as the packaging density resulting is increased as a result of miniaturization and thinning of the optical head.